ap chapter 12 notes 2

8/12/2019 AP Chapter 12 Notes 2

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Chapter 12 notes

The Cell Cycle


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The Key Roles of Cell DivisionCell division functions in reproduction,

growth, and repairUnicellular organisms (ex. Amoeba) will

divide to reproduce entire organismsCell division also will allows a multicellular

organism to develop from a single cell


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The Key Roles of Cell DivisionDNA is passed from one generation of

cells to the next without dilution.-cell duplicates it DNA- moves the 2 copies to opposite endsof the cell- and then splits into 2 daughter cells


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The Key Roles of Cell Division


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Concept 12.1Cell Division distributes identical sets of

chromosomes to daughter cells A cells genetic material is called its

genome- prokaryote = single long DNA strand- eukaryote = number of DNAmolecules


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Concept 12.1The replication and distribution of DNA is

manageable because it is packaged intochromosomes- the nuclei in human somatic cells contain 46 chromosomes- the nuclei in human gametes contains 23 chromosomes


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Concept 12.1


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Concept 12.1The DNA-protein complex is called the

chromatin and is a long thin fiber. After the chromatin is duplicated, it will

prepare for division. It will condenseand coil up to form chromosomes.


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Concept 12.1Each duplicated chromosome has 2 sister

chromatids .- each contains identical copies of thechromosomes DNA molecule - they are connected together at thecentromere


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Concept 12.10.5 m Chromosomes

Chromosomeduplication(including DNAsynthesis)

Chromo-some arm

Centromere

Sisterchromatids

DNA molecules

Separation ofsister chromatids

Centromere

Sister chromatids


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Concept 12.2The mitotic phase alternates with

interphase in the cell cycleThe mitotic (M) phase (mitosis and

cytokenesis) is the shortest part of thecell cycle.

Interphase accounts for about 90% ofthe cell cycle.


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Concept 12.2Interphase can be divided into subphases

- G1 (first gap), S (synthesis), and G 2 (second gap)- during subphases, cell grows byproducing proteins and organelles- chromosomes are only duplicatedduring the S phase


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Concept 12.2

S(DNA synthesis)

G 1

G 2


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Concept 12.2The cell moves into prometaphase

- nuclear envelope fragments- kinetochore attaches to formingspindles- cell prepares for metaphase


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Concept 12.2


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Concept 12.2Metaphase

- centrosomes area at opposite poles- chromosomes are on equator of cell,the metaphase plate

Anaphase - begins when the centromeres of thechromosomes separate


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Concept 12.2- sister chromatids begin movingtoward opposite poles- by the end, the poles have equal setsof chromosomes

Telophase- daughter nuclei form at the poles- nuclear envelope begins to reform


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Concept 12.2- chromosomes become less tightly

coiled-Cytokenesis, the division of the

cytoplasm, follows immediately


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Concept 12.2


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Concept 12.2The mitotic spindle distributes

chromosomes to the daughter cells-during interphase, the singlecentrosome replicates to form 2centrosomes; during the early stage of

mitosis, they separate and move towardopposite poles helping the spindle fibers


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Concept 12.2


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Concept 12.2Cytokenesis divides the cytoplasm

- in animals, cytokenesis occurs by theformation of a cleavage furrow- in plants the cleavage cannot occurbecause of the cell wall; vesicles willmove to the center of the cell to formthe cell plate .


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Concept 12.2

Cleavage furrow100 m

Contractile ring ofmicrofilaments

Daughter cells

(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

Vesiclesformingcell plate

Wall ofparent cell

Cell plate

Daughter cells

New cell wall

1 m


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Concept 12.2The origins of mitosis are believed to be from

bacterial organisms of cell reproduction- prokaryotes reproduce by binary fission(dividing in half) - prokaryotes do not have mitotic spindles;instead, once the DNA replicates, the copies ofthe region move apart rapidly


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Concept 12.2Origin ofreplication

Two copies

of origin

E . c o l i cell Bacterialchromosome

Plasmamembrane

Cell wall

Origin Origin


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Concept 12.3The cell cycle is driven by specific chemical

signals present in the cytoplasmSequential events of the cell cycle are directed

by a distinct cell cycle control system - driven by a built in clock- the cell cycle is regulated at certaincheckpoints by internal and external controls


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Concept 12.3


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The checkpoint is a control point wherestop and go-ahead signals can regulatethe cycle- kinases, a type of regulatory proteinthat activate or inactivate other

proteins, give the signals for G 1 and G 2 checkpoints

Concept 12.3


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Concept 12.3To be active the kinase must be attached

to a cyclin (kinases become cyclin-

dependent kinases or Cdks )- the activity of Cdks rises and falls withchanges in the [cyclin]

- first called MPF = maturationpromoting factor or M -phase-promoting factor


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Concept 12.3- when cyclins accumulate during G 2,MPF initiates mitosis

Internal and external cues help regulatethe cell cycle- for cells to divide a growth factor, aspecific protein, is released to stimulatecell division


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Concept 12.3The discovery of growth factors has led

us to understand density-dependentinhibition of cell division- when a cell population reaches acertain density, the amount of growth

factors and nutrients needed fordivision becomes insufficient forincreased growth


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Concept 12.3

Anchorage dependence

Density-dependent inhibition

Density-dependent inhibition

(a) Normal mammalian cells (b) Cancer cells25 m25 m


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Concept 12.3


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Concept 12.3- if cancer cells stop dividing, it is atrandom points and not at the

checkpointsCaner begins when a single cell tissue

undergoes a transformation

- if the cell evades destruction by theimmune system it may form a tumor


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Concept 12.3- if the abnormal cell remain at theoriginal site, it is called a benign

tumor- a malignant tumor becomesinvasive enough to impair the functionsof organs- the spread of cancer cells from theoriginal site is called metastasis


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Concept 12.3

ap chapter 12 notes 2

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